Tailscale has a pretty generous free tier AFAIK, and makes so much of managing a VPN like this dead simple. Plus if you ever want to mess with DIY, there's also headscale. I run headscale personally and it's solid, and works with the tailscale clients.

If your unsure how to set up public facing SSH… don’t. Your opening a possible attack vector. Use something like the free tier of Twingate.

You've gotten some good advice regarding VPNs, so I won't go into that, but if you do decide to open SSH or any other port, I would encourage you to spend some time setting up a firewall to block incoming connections. I have several services on HTTPS open to the world, but my firewall only allows incoming connections from whitelisted IP ranges (basically just from my cell phone and my computer at work). The number of blocked incoming connections is staggering, and even if they're not malicious, there is absolutely legitimate no reason for someone other than myself or the members of my household to be trying to access my network remotely.

Do you have ssh access running on local network? If so, all you have to do is forward the port. I'd recommend exposing a non-standard port, also using keys rather than password.

If you don't have your sshd running yet, it sounds like you need to read some guides to get a foundation, then come back with specific questions.

As you already have dynamic DNS set up, it should be as trivial as forwarding the ssh port (22).

I don't know what the default configuration of Raspbian is, but I would highly recommend generating an ssh key and disabling password login, if you're exposing your box to the internet.